[gst-devel] creating bins and ghostpads

[Andoni Morales]

2009/9/23 Rohan <rohan at perzonae.com>:
> Hi all,
>
> I am obviously doing something wrong here, but cannot figure out
> what.
>
> Essentially the pipeline is the same as the receiver but I have broken
> it into bins.  I seem to be having problems with the ghostpad, because
> I get this error:
>
> (stream_receiver.py:1914): GStreamer-WARNING **: Trying to connect elements that
> don't share a common ancestor: vidsource and vidbin
>
> Traceback (most recent call last):
>   File "stream_receiver.py", line 118, in <module>
>     server()
>   File "stream_receiver.py", line 27, in __init__
>     vidsource.link(vidbin)
> gst.LinkError: failed to link vidsource with vidbin
>
> Here is the code:
>
> ----------------------------------------------------------------------
> #!/bin/env python
>
> # The gst pipeline
> # pipe="udpsrc port=5000 ! smokedec ! autovideosink"
> # # audio
> # pipe="$pipe tcpclientsrc host=127.0.0.1 port=5001 ! "
> # pipe="$pipe speexdec ! queue ! alsasink sync=false "
>
> import sys,os
> import gobject
> import pygst
> pygst.require("0.10")
> import gst
>
> class server (object):
>        def __init__(self):
>                # start with video
>
>                self.pipe = gst.Pipeline("player")
>
>                # video source
>                vidsource = gst.element_factory_make("udpsrc", "vidsource")
>                vidsource.set_property("port", 5000)
>
>                vidbin = self.buildvid()
>                self.pipe.add(vidbin)
>                vidsource.link(vidbin)
You need to add vidsource to the pipeline prior to link it to any
other element. That's why GStreamer is complaining about vidsource and
vidbin not sharing a common ancestor.
Andoni
>
>
>                self.pipe.set_state(gst.STATE_PLAYING)
>
>        def buildvid(self):
>                bin = gst.Bin("vidbin")
>                queue = gst.element_factory_make("queue")
>                smokedec = gst.element_factory_make("smokedec")
>                vidsink = gst.element_factory_make("autovideosink")
>                bin.add(queue, smokedec, vidsink)
>                gst.element_link_many(queue, smokedec, vidsink)
>
>                # ghostpad
>                binsink = gst.GhostPad("binsink", queue.get_pad("sink"))
>                bin.add_pad(binsink)
>                return bin
>
> if __name__ == "__main__":
>        server()
>        loop = gobject.MainLoop()
>        loop.run()
>
> ----------------------------------------------------------------------------
>
> What is driving me slightly nuts is that if I put all the buildvid code
> into init and have a long series of object instatiations with add to
> pipeline and link it works, but as soon as I started messing with
> ghostpads and bin (which makes the code much more manageable when
> adding functionality for windows and macs) this messed up.  Below is
> more code that works, and I cannot figure out why this and why not
> that.
>
> And the other thing is this does work in a commandline pipeline such
> as the one sitting at the top of the script in comments.
>
> I am using the same system for the sender, but I'll only include the
> local display.  This sends an image happily, using the build_localvid
> bin, and linking it to the camera.
>
> -----------------------------------------------------------------------------
> #!/bin/env python
>
> import sys, os
> import gobject
> import pygst
> pygst.require("0.10")
> import gst
>
> class client(object):
>
>        def __init__(self):
>                self.pipe = gst.Pipeline("sender")
>
>                # Initial video input
>                camera = gst.element_factory_make("v4l2src", "camera")
>                vidtee = gst.element_factory_make("tee", "vidtee")
>                self.pipe.add(camera, vidtee)
>                camera.link(vidtee)
>
>                # local video
>                localvidbin = self.build_localvid()
>                self.pipe.add(localvidbin)
>                vidtee.link(localvidbin)
>
>                self.pipe.set_state(gst.STATE_PLAYING)
>
>        def build_localvid(self):
>                """This bin takes a camera (video) stream and produces a live image locally."""
>                bin = gst.Bin("localvid")
>                queue = gst.element_factory_make("queue")
>                out = gst.element_factory_make("xvimagesink")
>                bin.add(out, queue)
>                queue.link_pads("src", out, "sink")
>                binsink = gst.GhostPad("binsink", queue.get_pad("sink"))
>                bin.add_pad(binsink)
>                return bin
>
> if __name__ == '__main__':
>        client()
>        loop = gobject.MainLoop()
>        loop.run()
>
> ---------------------------------------------------------------------------
>
> This does the correct thing, and I get a live image from the camera.
>
> I am completely stumped on this one, and have resorted to using
> gst.parse_bin_from_description() with the gst-launch pipeline, but
> this is far from ideal from a maintenance perspective. :)
>
> I am sure I am missing something pretty obvious, but so far flailing
> around in my ignorance has not let me stumble on a solution.
>
> Thanks for any help,
>
> Rohan
>
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-- 
Andoni Morales Alastruey

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